1. Field of the Invention
This invention relates to a motor driving apparatus for driving a motor with error detection.
2. Description of the Prior Art
A motor driving apparatus for driving a dc motor as a power source of a cooling fan mounted on a motor vehicle, is known. In this motor driving apparatus, a switching element is provided on the line between the battery and a dc motor mounted on the motor vehicle. The switching element turns on and off with duty control, that is, pulse width modulation (PWM) to smoothly control the rotation speed of the dc motor.
Another motor driving apparatus with error detection such as disconnection of the line between the battery and the dc motor or shorting to the ground, is known. Japanese utility model application provisional publication No. 56-141530 discloses such a prior art motor driving apparatus including a resistor provided on the line between the dc motor and the battery. The error is judged by detecting whether the voltage difference between both ends of the resistor exceeds a predetermined voltage during driving the motor to detect whether or not the driving current normally flows.
FIG. 5A is a block diagram of the prior art motor driving apparatus having a current detection resistor. The current detection resistor RS is provided on the current path between the dc motor 2 and the battery 4. The voltage difference is detected by a disconnection/shorting detection circuit 60. In this circuit, the driving current flows through the current detection resistor Rs.
Another type of a prior art motor driving apparatus is shown in FIG. 5B. In this motor driving apparatus, a current detection resistor Rse is provided on a bypass line of the line between the dc motor and the ground. More specifically, a multi-drain FET is used for PWM switching. One drain is used for switching a main part of the driving current. Another drain passes a remaining part of the driving current. The remaining part of the driving current flows through the current detection resistor Rse. A disconnection/shorting detection circuit 61 detects the voltage difference. In this circuit, a part of the driving current flows through the current detection resistor Rse. Thus, power loss is reduced. In both motor driving apparatuses shown in FIGS. 5A and 5B, on occurrence of errors of disconnection and shorting, alarm signals are generated.
Moreover, in both motor driving apparatuses shown in FIGS. 5A and 5B, the dc motor 2 coupled to a cooling fan may be driven by the cooling fan due to wind. In this condition, the dc motor generates electromotive force that may reduce the driving current flowing through the dc motor. So the disconnection/shorting detection circuit 60 or 61 may erroneously detect error in the current path of the dc motor 2.
The aim of the present invention is to provide a superior motor driving apparatus.
According to the present invention, a first aspect of the present invention provides a dc motor driving apparatus comprising: switching means provided at a first current path between a dc power supply and a dc motor; control means for generating a pulse width modulation signal to turn on and off said switching means in response to a control signal; detection means for detecting a voltage at a second current path between said dc motor and said switching means, said first current path including said second current path; and judging means for judging whether said voltage from said detection means varies at a first cycle which is substantially the same as a second cycle of said pulse modulation signal and judging that there is an error on a third current path from said dc power supply to said switching means via said dc motor when said voltage from said detection means does not vary at said first cycle which is substantially the same as said second cycle of said pulse modulation signal.
According to the present invention, a second aspect of the present invention provides, in a motor driving apparatus comprising: switching means provided at a first current path between a dc power supply and a dc motor; control signal generating means in response to a control signal for setting a target driving voltage for said dc motor and generating a pulse width modulation signal for controlling a driving voltage for said dc motor toward said target driving voltage as a control signal; and driving means for rotating said dc motor by turning on and off said switching means in accordance with said control signal, the improvement comprising; detection means for detecting a voltage at a second current path between said dc motor and said switching means, said first current path including said second current path; and judging means for judging whether said voltage from said detection means varies at a first cycle which is substantially the same as a second cycle of said pulse modulation signal and judges that there is an error on a third current path from said dc power supply to said switching means via said dc motor when said voltage from said detection means does not vary at said first cycle which is substantially the same as said second cycle of said pulse modulation signal.
According to the present invention, a third aspect of the present invention provides a motor driving apparatus based on the first aspect, further comprising a resistor connected to electrodes of said switching means in parallel, wherein a resistance of said resistor is determined such that a current flowing through said resistor does not rotate said dc motor when said switching means is in an OFF condition.
According to the present invention, a fourth aspect of the present invention provides a motor driving apparatus based on the first aspect, wherein said judging means comprising: first judging means for judging whether variation in said voltage from said detection means tracks variation in a voltage of said control signal; and second judging means for monitoring an interval for which said variation of said detection voltage does not track said control signal and judging that there is said error on a current path from said dc power supply to said switching means via said dc motor when said interval exceeds a predetermined judging interval.
According to the present invention, a fifth aspect of the present invention provides a motor driving apparatus based on the first aspect, wherein said switching means comprises a plurality of switching elements, and said detection means comprising a plurality of detection elements, each of said switching elements provided at said first current path, each of said detection elements detects said voltage at said second current path, each of said first current paths including each of said second current paths, and said judging means judges that there is an error on any of said third current paths from said dc power supply to a plurality of said switching means via said dc motors when any of said voltages from said detection means does not vary at said first cycle which is substantially the same as said second cycle of said pulse modulation signal.
According to the present invention, a sixth aspect of the present invention provides a motor driving apparatus based on the first aspect, wherein said dc motor is mounted on a mobile unit and provided for rotating a fan which is further rotated by a wind generated by movement of said mobile unit.
According to the present invention, a seventh aspect of the present invention provides a motor driving apparatus based on the fifth aspect, wherein said dc motors are mounted on a mobile unit and provided for rotating fans, respectively, which are further rotated by wind generated by movement of said mobile unit.
According to the present invention, an eighth aspect of the present invention provides a motor driving apparatus comprising: switching means provided at a first current path between a dc power supply and a dc motor; control means for generating a pulse width modulation signal to turn on and off said switching means in response to a control signal; detection means for detecting a voltage at a second current path between said dc motor and said switching means, said first current path including said second current path; and judging means for judging whether said voltage from said detection means and said pulse width modulation signal correspondingly vary each other in variation cycle and judging that there is an error on a third current path from said dc power supply to said switching means via said dc motor when said voltage from said detection means and said pulse width modulation signal does not correspondingly vary each other in variation cycle.
According to the present invention, a ninth aspect of the present invention provides a motor driving apparatus comprising: switching means provided at a first current path between a dc power supply and a dc motor; control means for generating a pulse width modulation signal to turn on and off said switching means in response to a control signal; detection means for detecting a voltage at a second current path between said dc motor and said switching means, said first current path including said second current path; and judging means for judging whether variation in said voltage from said detection means tracks variation in said pulse width modulation signal and judging that there is an error on a third current path from said dc power supply to said switching means via said dc motor when said variation in said voltage from said detection means does not track said variation in said pulse width modulation signal.